1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus for use in an ink jet printer, and particularly to those in a bubble jet recording method in which a bubbling phenomenon is used.
2. Description of the Related Art
An ink jet recording head in a bubble jet recording method generally comprises fine discharge ports, flow paths, and heat generating members provided in a part of the flow paths. In a bubble jet recording method, bubbles are generated by locally increasing a temperature of a liquid in a flow path using a heat generating member, the liquid is extruded from a fine discharge port by utilizing a high pressure at the bubbling, and then droplets of the liquid are deposited to a recording sheet or the like.
To obtain a finer image recorded in this bubble jet recording method, there is a need for a technology of discharging fine droplets at a high density. Therefore, it is particularly important to form fine flow paths and fine heat generating members. Accordingly, there has been suggested a method of manufacturing a head which enables a high-density arrangement by making the most of the photolithography technology with utilizing simplicity of a structure of the bubble jet recording system (for example, Japanese Patent Application Laid-Open No. 08-15629). In addition, to adjust a discharge amount of droplets, there has been suggested a heat generating member having a large heat release value in its central portion in comparison with its end portions (Japanese Patent Application Laid-Open No. 62-201254).
As a heat generating member, generally is used a tantalum nitride thin-film resistor having a thickness of approximately 0.05 xcexcm and a Joule heat at energizing it is used to bubble the liquid. This kind of heat generating resistor is generally provided with a cavitation resistive layer made of a metal such as Ta having a thickness of approximately 0.2 xcexcm through an insulating layer such as SiN having a thickness of approximately 0.8 xcexcm to prevent a surface of the heat generating resistor from being damaged by a cavitation.
Furthermore, in Japanese Patent Application Laid-Open No. 64-20150, there is disclosed a multi-nozzle ink jet head wherein a plurality of vertical wires and a plurality of horizontal wires are arranged on a PC board and intersections of the both are provided with rectifying elements into which only forward current flows and heating elements connected thereto. In addition, in Japanese Patent Application Laid-Open No. 57-36679, there is disclosed a thermal head having a PC board on which there are a plurality of diodes arranged in arrays which enables a heat generation by energizing in the forward direction.
In a lot of conventional ink jet recording heads, heating elements, diodes, and logic circuit portions are fabricated at a time on a silicon base by a semiconductor process (ion implantation or other method). Therefore, a head having a relatively small number of nozzles can be compact in size, thereby enabling the fabrication in a single process advantageously. However, a full-line multi-head having a length of a full sheet width, for example, requires a length of approximately 12 inches (about 30 cm) and therefore an attempt of integrally assembling it may increase a cost since it is hard to use a normal silicon wafer.
Accordingly, if the heating elements for the bubble jet recording arranged in a matrix can be selectively driven by using nonlinear elements which can be generated without a use of the conventional semiconductor process such as the ion implantation method, it may be possible to provide a continuous ink jet recording head at a low cost.
Conventionally, MIM elements or the like which are nonlinear elements are used for liquid crystal devices. If the MIM elements are used for a liquid crystal device, a normal power density is approximately 1 W/m2. On the other hand, approximately 0.1 GW/m2 or higher power density need be treated for a heat generating member of a bubble jet recording head. Therefore, when an attempt is made to use the MIM elements as heat generating members of the bubble jet recording head, conventionally much more power need be supplied to resistive elements connected in series to the MIM elements, in comparison with the power used for the liquid crystal device. To solve this problem, it is possible to increase the power that can be supplied to the MIM elements to some extent by increasing a voltage applied to the MIM elements. There is, however, a fear of causing the MIM elements to be destroyed by a temperature rise of the MIM elements due to a heat generation thereof. There is no problem in this heat generation of the MIM elements in the conventional configuration in which the MIM elements are assumed to be nonlinear elements for matrix driving such as a case where the MIM elements are used for a liquid crystal device, while, if the MIM elements are used as nonlinear elements for matrix driving of heat generating members of a bubble jet recording apparatus, there is a fear of causing the MIM elements to be destroyed by the heat generation of the MIM elements as its own peculiar problem.
Therefore it is an object of the present invention to provide an ink jet recording head and an ink jet recording apparatus which can be manufactured at low cost and with a continuous length by using nonlinear elements having MIM-type electrical characteristics to drive heat generating members having a bubble jet recording system so as to prevent the nonlinear elements from being destroyed by a heat generation of the nonlinear elements.
According to one aspect of the present invention, there is provided an ink jet recording head comprising heating means each having a heat generating resistor generating a heat energy used for discharging ink and a pair of electrodes connected to the heat generating resistor and nonlinear elements connected in series to the heat generating resistors to drive the heat generating resistors and having MIM-type electrical current and voltage characteristics in which a resistance value at a low voltage is higher than one at a high voltage independently of a polarity, wherein an area of the nonlinear element is larger than that of a portion between the pair of electrodes of the heat generating resistor. This arrangement prevents the nonlinear elements from being destroyed by a heat generation of the nonlinear elements.
Furthermore, preferably the area of the nonlinear element is 3.7 to 108 times larger than that of the portion between the pair of electrodes of the heat generating resistor. This prevents the nonlinear elements themselves from being destroyed by a heat generation thereof and it does not hinder downsizing of the head. Furthermore, it enables a supply of a large current necessary for bubbling a liquid for discharging while lowering a driving voltage to such an extent that it does not increase an element driving cost.
In addition, preferably a length of the nonlinear element in the discharge port arrangement direction is shorter than a length of it in a direction substantially orthogonal to the arrangement direction. This enables the discharge ports and the nonlinear elements to be arranged at a high density.
Furthermore, the arrangement may be such that the nonlinear element is formed on the same PC board as for the heat generating resistor, having a discharge port formed substantially in a direction perpendicular to the PC board and that a flow path extends mainly on the opposite side to a position where the nonlinear element is arranged from the position where the heat generating resistor is formed. Otherwise, the arrangement may be such that the nonlinear element is formed on the same PC board as for the heat generating resistor, having a discharge port formed substantially in a direction parallel to the PC board and that the flow path extends mainly on the same side as the position where the nonlinear element is arranged from the position where the heat generating resistor is formed. In both cases, the nonlinear element having a large area can be arranged without hindering the liquid discharging.
Still further, an arrangement of a cooling structure for the nonlinear element prevents the nonlinear element from being destroyed by a heat generation thereof more reliably.
Preferably, a resistance value of the nonlinear element in a driving state is substantially equal to that of the heat generating resistor.
Furthermore, the present invention may include matrix electrodes constituting a matrix circuit for applying a voltage to the heating means. Additionally, the nonlinear element may be located at an intersection of the matrix electrodes.
An ink jet recording head according to the present invention may have such a mechanism that ink is discharged by causing film boiling in the ink by means of the heat energy.
An ink jet recording apparatus according to the present invention comprises at least an ink jet recording head having one of the above arrangements, being provided with ink discharge ports for discharging ink as opposed to a record area of a recording medium, and feeding means.